Layers of fabric material are frequently laminated or otherwise joined together to produce fabrics having desirable characteristics not fully exhibited by the layers individually. Such is the case with fabrics made of elastomeric polymers, which by themselves exhibit desirable stretch and springback properties, but are not pleasant to touch or be next to the skin for extended periods of time. Thus, techniques have been developed to make stretchable laminates with soft nonwoven fabrics, e.g., stretch bonded laminate and necked spunbond laminate technology. The present commercial processes to make these laminates places the soft facings on both top and bottom faces of the elastomeric sheet.
Bonding of two dissimilar materials requires that the two materials be adhered to one another in some manner. Where the two materials exhibit natural adhesive or attractive characteristics, bonding does not require significant specific treatment. An example of two such materials is polypropylene spunbond and KRATON.RTM. G2755 elastomer, available from Shell Chemical Company, Houston, Tex., as described hereinbelow. However, where the materials do not exhibit such attraction to each other, the molten elastomeric layer may be mechanically forced into the nonwoven material fabric structure, encapsulating the fibers, to create the bonding. Such penetration is typically achieved by passing the two layers to be laminated, usually while the elastomeric layer is still molten, through a niproll assembly comprised of two substantially flat rolls, whereby the niprolls apply even pressure across the surface of the two layers to bond the surfaces together. Bonding is achieved by the niproll pressure forcing the molten elastomeric material deep into the nonwoven fiber matrix, encapsulating the fibers. The interply attachment, as measured by the peel strength of a necked bonded laminate ("NBL"), has been found to increase as the elastomeric film polymer penetrates into the nonwoven layer. Unfortunately, the elastic properties deteriorate as this penetration is increased because fiber independence to move freely is reduced by the infusion of the encapsulating elastomer. If the nip gap is increased, elastic properties improve, but interply attachment decreases because there is less elastomer penetration into the nonwoven material and peel test performance suffers. Thus, a niproll assembly having two substantially flat rolls, while useful for many processes, can produce laminates having less than optimum qualities. What is needed is a process using a niproll assembly that would produce a laminate having sufficient bonding area while maintaining fiber independence so as to maintain desirable elasticity and peel properties. Additionally, it would be desirable to have a process and a laminate formed therefrom that would maintain the elastic properties while resulting in a soft material and laminate integrity.
It has also been frequently found useful to add a tackifier to the elastomer to increase bonding by making the elastomer stick to the nonwoven layer so penetration and encapsulation are not required. A single spunbond faced necked bonded laminate or stretch bonded laminate could be made with this tackified elastomer but the exposed elastomer face could stick to the nonwoven layer on the next wrap when it is wound into a roll and then the roll could not be unwound. It would be desirable to have an clastomer composition that would facilitate bonding, but would not cause the laminate layers to stick together during "in-roll" conditions. Also, total attachment between spunbond and tackified elastomer would reduce elasticity properties.
Accordingly, it is an object of the present invention to provide a laminated fabric having desirable elastic integrity and feel characteristics.
It is another object of the present invention to provide a laminated fabric whereby at least two layers of the laminate are point embossed together to provide selected areas of bonding and selected areas of free fiber movement.
It is a further object of the present invention to provide a laminated fabric that can be wound on a take up roll yet have reduced sticking between roll windings.
Other objects, features, and advantages of the present invention will become apparent upon reading the following detailed description of embodiments of the invention, when taken in conjunction with the accompanying drawings and the appended claims.